1. Field of the Invention
The present invention relates to a system for controlling a motor, and more particularly to a system for controlling a motor, for removing speed ripples generated when controlling the motor and noise generated when driving the same, wherein the speed ripples are caused by loads generated when driving a single rotary compressor.
2. Description of the Related Art
Typically, in order to control a motor, there is a need for a motor control system to recognize speed information or magnetic flux information of the motor. A conventional motor control system has adapted a speed sensor, such as a resolver or pulse encoder, or a magnetic flux sensor to recognize the speed information and magnetic flux information, but these sensors have difficulty in their installation and are greatly affected by their installation environment, thereby unavoidably increasing the cost of production.
Therefore, there have been increasingly developed a variety of control systems for controlling the speed of the motor without using the speed sensor and the magnetic flux sensor. As shown in FIG. 1, a sensorless control system for the synchronous reluctance motor includes a three-phase voltage generator 3 for outputting a three-phase voltage to an inverter 2 driving the motor 1, an estimation unit 4 for estimating a rotor speed and rotation angle of the motor 1 upon receiving currents iu and iv transmitted from the inverter 2 to the motor 1, a first subtracter 5 for generating a difference between a reference speed xcfx89* of the motor 1 and an estimated speed {tilde over (xcfx89)} generated from the estimation unit 4 by subtracting the estimated speed {tilde over (xcfx89)} from the reference speed xcfx89*, and a speed controller 6 for generating a reference torque current i*q on the basis of the difference between the reference speed xcfx89* and the estimated speed {tilde over (xcfx89)}.
The sensorless control system for the synchronous reluctance motor further includes a fixed/rotation coordinates converter 7 for converting a value estimated by the estimation unit 4 into values id and iq of a rotation coordinates system, a second subtracter 8 for generating a difference between the reference torque current i*q and an output value of the fixed/rotation coordinates converter 7, a magnetic flux command generator 9 for generating a reference magnetic flux current i*d according to the estimated speed {tilde over (xcfx89)}, a third subtracter 10 for generating a difference between the reference magnetic flux current i*d and a real magnetic flux current id, a current controller 11 for generating a reference magnetic flux voltage V*d and a reference torque voltage V*q upon receiving output signals from the second subtracter 8 and the third subtracter 10, and a rotation/fixed coordinates converter 12 for converting an output value of the current controller 11 into values V*xcex1 and V*xcex2 of a fixed coordinates system.
However, a single rotary compressor has load characteristics variable with a rotation angle of a motor as shown in FIG. 2a, such that speed characteristics of the motor are plotted on a time axis (t) as shown in FIG. 2b. In more detail, as compression and expansion strokes are performed simultaneously with driving vanes of the compressor, there may occur ripples of 60-100 rpm, shown in FIG. 2b on the time axis (t), on which the speed characteristics of the motor is plotted, such that these ripples result in undesired vibrations or noise of a compressor and performance deterioration thereof.
Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a system for controlling a motor, which removes ripples that may deteriorate a motor""s speed characteristic due to loads generated when driving a single rotary compressor, such that it removes vibrations or noise of a compressor and prevents a performance of the compressor from being deteriorated.
In accordance with the present invention, the above and other objects can be accomplished by the provision of a system for controlling a motor, including: a three-phase voltage generator for outputting a three-phase voltage to an inverter driving a motor; a rotation/fixed coordinates converter for converting a reference magnetic flux voltage and a reference torque voltage of a rotation coordinates system of the motor into data of a fixed coordinates system, and outputting the data to the three-phase voltage generator; a fixed/rotation coordinates converter for converting a three-phase current applied from the inverter to the motor into a two-phase current so as to convert currents of the fixed coordinates system into currents of the rotation coordinates system; an estimation unit for estimating a rotation angle and rotor speed of the motor upon receiving currents applied to the fixed/rotation coordinates converter; and a control block for receiving the estimated rotation angle and the estimated speed from the estimation unit, outputting the reference magnetic flux voltage and the reference torque voltage, in which an error caused by loads when driving the motor is compensated, to the rotation/fixed coordinates converter.